The invention is relevant to the field of herbicides, in particular to dry formulations of herbicides such as wettable powder, water-dispersible granular, and powder suspension herbicidal compositions.
Bromoxynil (Ia), a member of the benzonitrile class of photosystem II inhibitors, is a well-known anti-dicot herbicide. It is available in several forms, each of which is associated with certain advantages and disadvantages. Bromoxynil itself, as a free phenol, has good physical properties but is not especially active. The activity of bromoxynil can be improved by formation of ester derivatives. Bromoxynil octanoate (Ib), for example, is more active, but it is less selective; it is also low-melting (m.p. 45-46xc2x0 C.) and difficult to formulate without fillers or solvents. Bromoxynil butyrate (Ic) is more active than the octanoate, but even less selective, and due to its low melting point it is again necessary to employ organic solvents or fillers in preparing formulations for commercial use. The lower selectivity of the esters leads to a greater degree of damage to crop species, particularly corn, when compared to the free phenols. 
Ioxynil and ioxynil octanoate (IIa and IIb) have similar properties, and similar issues arise with respect to processing and formulating these materials.
Low-melting herbicides may be converted into a solid form by intimate admixture with an inert filler or carrier, such as a clay or silica. For example, U.S. Pat. No. 5,374,607 (incorporated herein by reference) discloses a method of dispersing herbicides on a finely powdered carrier by first dissolving or melting the herbicide ingredient(s), and applying the herbicide(s) in liquid form to the carrier. A similar method of dispersing molten trifluralin on calcium carbonate is described in EP 124,993, and British patent GB 1,293,515 describes melting together propachlor (m.p. 67-76xc2x0 C.) and atrazine, and dispersing the resulting melt onto attapulgite granules. These methods do avoid the grinding step, and thereby avoid problems with softening or melting of ingredients during grinding, but the presence of a filler leads to compositions having less active ingredient per pound, and requiring correspondingly more resources to package, transport, store, and dispense the final herbicidal product.
Low-melting herbicides may also be microencapsulated by dispersion of the melted substance in an aqueous solution of a film-forming polymer, followed by spray-drying, as described in U.S. Pat. No. 5,160,530 for the low-melting herbicide trifluralin (m.p. 41-43xc2x0 C.). Microencapsulated alachlor and acetochlor have been combined with atrazine in wettable powder or granular compositions, as described in U.S. Pat. No. 4,936,901, incorporated herein by reference. Spray-drying and microencapsulation, however, entail additional capital expenses for the necessary machinery, and incur energy and other processing costs.
European patent EP 404,201 describes a process of dispersing molten pendimethalin in water, and cooling the resulting suspension, but there is no disclosure that the resulting suspension can be converted into a wettable powder or granular form. German patent DE 3,702,604 describes a similar process in which molten pendimethalin is dispersed into a suspension of atrazine; again there is no disclosure that the resulting suspension can be converted into a wettable powder or granular form.
There remains a need, therefore, for solid forms of low-melting phytopharmaceutical agents, such as bromoxynil and ioxynil, which retain the performance advantages of the agents but which do not have the processing and formulation disadvantages associated with a low melting point.
The invention provides co-melts, or alloys, of bromoxynil and ioxynil esters and other low-melting or liquid phytopharmaceutical agents, with higher-melting additional active ingredients. The low-melting phytopharmaceutical agent is preferably a bromoxynil ester. The additional active ingredients may be other pesticides, and are preferably other herbicides. The alloys of the invention are sufficiently high-melting that they may be processed and formulated in a conventional manner without difficulty. In particular, dry formulations, such as wettable powder formulations may be readily produced from the alloys by routine methods, for example by dry grinding or jet-milling the alloys of the invention, without excessive use of inert carriers or fillers. The resulting formulations can therefore contain a higher percentage of active ingredient.
An additional advantage of the invention is improved selectivity of herbicidal compositions which are prepared from the alloys of the invention. It has unexpectedly been found that a formulation of an alloy of the invention is more selective in its herbicidal effects than a comparable formulation containing the same components in a non-alloyed form.
Formulations of the invention comprising bromoxynil octanoate and atrazine are particularly useful for prevention of weed growth, either pre- or post-emergence, in crops such as cotton, cereals, corn and other maize crops, rice, sorghum, alfalfa, mint, onions, garlic, and shallots; and for weed control in pasture and turf areas.